Characterizing streambed water fluxes using temperature and head data on multiple spatial scales in Munsan stream, South Korea

Accurate characterization of water fluxes in the streambed where surface water–ground water (SW–GW) interacts is essential to evaluate the fate and transport of a contaminant plume and to investigate aquatic ecosystems in aquifers connected to rivers or streams. Vertical streambed water fluxes were characterized on multiple spatial scales using temperature-depth profiles and head data measured in a reach of Munsan stream, Paju-si, South Korea. This study applied an exponential model and type curves to determine water fluxes on a large scale of aquifer thickness including a streambed (=15 m) under the assumption of steady state heat transport. On a small scale of the streambed (=0.3 m) Darcy’s law was used to calculate water fluxes through the streambed. The results showed that regional ground water discharges occurred to the stream through the streambed over the reach considered in both August, 2008 and January, 2009 while significant spatial variability in vertical streambed fluxes was found for the streambed of 0.3 m in thickness due to heterogeneities in streambed hydraulic conductivity, variations in stream discharge, and hydraulic gradients in the streambed. Therefore, it is concluded that vertical water fluxes in the streambed of the site are affected by regional ground water flow moving from a deep aquifer to stream and by local small-scale upward or downward hyporheic flow simultaneously. From seepage flux estimates and electrical conductivity (EC) data of water samples, the origins of water in the streambed were inferred. It suggested that SW–GW mixing zones were present at 0.3 m deep or probably even deeper streambeds at S3–S5 located in mid- to downstream at the site. Results have significant implications on effective water resources managements and aquatic habitat investigations in ground water dependent ecosystems of the site.